Oscillation generator



J. w. HORTON OSCILLATION GENERATOR sew. 1926. v mama Original Filed A rii 18, 1922 fatented Sept. 28, 126.

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JOSEPH W. HORTON, OF BLOOMFIELD, NEW JERSEY, ASSIGN'OR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED,

A CORPORATION OF NEW YORK.

OSGILLATION GENEBATOR.

Application filed April 18, 1922, Serial No. 555,286. Renewed December 5, 1925.

This invention relates to a method of and means for generating electric oscillations.

()ne object of this invention is to provide an arrangement for producing electric oscillations of a single frequency. Another object is to generate oscillations of pure wave form. Still another object is to provide an oscillator which is exceptionally stable under variable operating conditions.

Briefly described, the present invention comprises an electric discharge device provided with a heated cathode, an anode, and a control element or grid, having an output 011'- cuit connected between the cathode and anode coupled in feed back relation with an input circuit connecting the cathode and grid, and a second electric discharge device, controlled by the first, adapted tosupply oscillations to a load circuit.

More specifically the output circuit of the oscillating discharge device is divided into two branches through one of which direct current potential is impressed upon its anode, while the other branch constitutes an oscillating current path. The oscillating current branch includes a high resistance and a frequency determining tuned circuit including an inductance shunted by capacity either or'both of which may be variable. The tuned circuit is coupled with the input circuit by a transformer having a high coefficient of coupling, e., the ratio '\/L1L2 is large, where M represents the mutual inductance between the transformer windings, and L and L the self-inductances of the respective windings, whereby an efficient transfer of energy between the tuned circuit and input circuit may be effected without distortion, for whereas close feed back coupling would not be possible with the ordinary oscillator, because of the distortion occasioned by overloading the discharge device, the controlling resistance of applicants oscillator permits the feed back coupling tobe made as close as possible without danger of overloading the device. The control electrodes of the two discharge devices are connected to the secondary winding of the coupling transformer in parallel relation and the filaments are connected in series with a source of heating current. Plate potential is. supplied to both devices from a single source through paths which offer high impedance to the oscillating current and the output circuit of the second device is connected to a load circuit through a potentiometer.

The purpose of the preceding statement is to outline briefly and describe in a general way one practical arrangement embodying the principles of the present invention which will be set forth in detail in the following description, and it is, therefore, not to be interpreted as defining the scope ofthe invention. The novel features and combinations which are believed to be characteristic of this invention will be set forth with particularity in the appended claims.

The invention itself however, both as to its organization and method of operation will be best understood by reference to the following description read in connection with the attached drawings in which, ig. 1' shows an oscillator designed in accordance with this invention and Fig. 2 illustrates the filament heating circuit for the several discharge devices shown in Fig. 1.

The arrangement shown in Fig. 1 embodies an oscillator designed in accordance with this invention connected by a potentiometer to the input circuits of two parallel connected amplifiers, the output circuits of which are in turn connected to a load cir-.

cuit. The oscillator comprises two discharge devices 1 and 2 each having a cathode, an anode and a control element or grid. The cathodes or filaments of the two devices are connected in series with the heating source 3 and are shunted by a resistance 4 for a purpose to be hereinafter referred to. The input circuit of the first or oscillating device 1, which includes a coil 5, is connected .between its cathode and control element. The output circuit, connecting the cathode and anode of this device, is provided with two branches 6 and 7. The source 8, in cluded in the branch 6, supplies space current to the device 1 through the retard coil 9, adapted to interpose a high impedance to the flow of oscillating current. The oscillating current branch 7 includes a block ing condenser 10, which serves to prevent the flow of," direct current through .this branch, high resistance 11 and a tuned circuit 12, comprising a coil 13 shunted by a variable condenser 14, for determining the frequency of the oscillations generated. The

7 device 2 being completed through the coil 5 and the filament of the device 1, and hence the polarizing potential normally impressed upon the control element of the device 2 will be determined by the drop of potential across the filament of the device 1. Thus the control elements are connected in parallel to the secondary winding of the feed back transformer 13-5, and the fluctuating potentials impressed upon the control elements of both devices will be the same as to wave form and amplitude.

Plate potential is supplied to the amplifying device 2 from the source 8 through a retard coil 16 which offers high impedance to the oscillating current. Amplified oscillating current flows through the resistance 17 included in a second or oscillating current path associated with the output circuit of the amplifier 2. A movable contact element l8 engages the resistance 17 and is adapted 'to provide means whereby the potential impressed upon the control elements of the parallel connected amplifiers 19 and 20 may be varied. Space current is supplied to amplifiers 19 and 20 from the source 8 through a retard coil 21 adapted to impose a high impedance to the flow of oscillating current, and the amplified oscillating current flows through a path coupled to a load circuit by the transformer 22. A blocking condenser 23 is included in the oscillating current output path of these amplifiers to prevent the flow of direct current from the source 8 through the primary of the trans former 22.

As thus far described it will be seen that the entire oscillating current energy of the first or oscillating device flows through the high resistance 11 to the tuned circuit 12 in which oscillations of the frequency determined by the constants of this tuned circuit will be produced. Resistance 11 serves to limit the amplitude of the current fed back to such value that the operation of the device 1 is confined. to the linear portion of its input-voltage-output-current characteristic curve. The value of resistance 11 is fixed for a given frequency range. For other frequency ranges a fixed resistance of different value for each range is used. Obviously this may be effected by using a single resistance element adapted to be varied to provide the desired values for a plurality of frequency ranges, or different resistance units of proper values may be substituted for one another when necessary. By virtue of the coupling between the coils 13 and 5 potential variations of the frequency determined by the circuit 12 will be impressed upon the grids of the devices 1 and 2, thereby controlling the supply of oscillating current to the feed back circuit of device 1 and through the potentiometer 17-18 to the input circuits of the amplifiers 19 and 20.

As is well known, oscillators comprising electric discharge devices having input and output circuits coupled in feed back relation generally produce a complex wave which upon analysis, is found to consist of a wave of the frequency determined by the tuned circuit included in the circuit system associated with the discharge device and other wave components harmonically related to that of the determined or fundamental frequency. In general these harmonics result from the distorting efiect of the device, or in other words, they are due to the fact that the relation between the inputvoltage and the output-current for the operating range of the discharge device used is not linear.

With the object of eliminating the distortion introduced by the discharge device, it has hitherto been proposed to insert a resistance, in the space current branch of the output circuit of an oscillator having a frequency determining circuit included in its plate circuit, or in a portion of the output circuit of an oscillator of this type which is common to both the space current and oscillating current, but external to the tuned circuit. In this manner, it has been proposed to limit the operation of the oscillating device to the linear portion of its operating characteristic, by regulating the amplitude of the direct current supplied to the device in the first case, or the amplitudes of both the direct and oscillating currents in the second case. The present invention provides an arrangement which is especially adapted to prevent overloading of the oscillating device, whereby the frequency of the output energy may be maintained constant, and the wave form of the oscillating current may be practically sinusoidal.

For the best results, discharge devices 1 and 2 should have the same physical characteristics, the coeflicient of coupling between the coils 13 and 5 should be large, the control elements of devices 1 and 2 should be connected in parallel to the secondary of the feed back transformer, the time constant of the coil 13, i. e. ratio of its inductance to its resistance, should also be large, the magnitude of the feed back resistance 11 should be high, and the filament and grid of the oscillating device should normally be at the same potential. Under these conditions the percentage of harmonically related energy generated will'be a minimum for the arrangement shown.

It has been experimentally determined that if the value of the feed back resistance and the physical characteristics of the tube are properly related, the frequency of the waves produced by an oscillator of this design is independent of. the resistance through a wide frequency range. There is a minimum magnitude of feed back resistance 11 that should be used with each coupling transformer and, since both the first and second harmonics are reduced by increasing the feed back resistance, it is desirable to make this resistance as .high as possible.

Experiments were made with an oscillator of the design herein described including electrio-discharge devices, having physical characteristics such that when a heating current of 1.3 amperes is supplied to the filament, a plate potential of 100 volts isimpressed upon the anode, and no polarizing potential is impressed upon the grid, the internal plate circuit impedance of each device is of the order of 5000 ohms. The input and output circuits of the first device were coupled in feed back relation by a transformer 'having a coefficient of coupling of .65, the time constant of the primary winding of the transformer included'in the fre uency de termining circuit was .625, a' fee back resistance of 144,000 ohms was used, and oscillations of 10,000 cycles were supplied to a load circuit of 200 ohms resistance through a step down transformer having a transformation ratio of approximately 11. Under these conditions, when the plate battery was varied from 104 to 128 volts' a change in the .frequency of the oscillations generated of .05% occurred, and when the filament heating current was varied from 1.2 to 1.4 amperes, the frequency of the oscillations generated varied .02%. The output current changed 1% when the platev potential was varied over the range given above, and though the filament heating current was varied from 1.08 to 1.45 amperes the amplitude of the alternating output current remained substantially constant.

When a common source is used to supply. heating currentto the filaments of the several devices shown in Fig. 1 their filaments are preferably'connected as shown therein.

The filament heating circuit is clearly shown in Fig. 2. As, therein illustrated the filaments of the first and second devices are connected in series and in shunt to a resistance 4, which is equal in magnitude to that of the two filaments in series. The filaments of the third and fourth devices, 19 and 20, are connected in parallel with each other, and in series circuit with the filaments of the two first mentioned devices, 1 and 2. By the in- From the data given above it will be apparent that, by including a high resistance in the feed back circuit between the anode and frequency determining circuit of the oscillating device, the frequency and amplitude of the current supplied by the oscillator to a load circuit are maintained substantially constant. Again, b connecting the grids of the oscillating and rst amplifying tubes directly together and to the frequency determining circuit, as described above, this circuit operates as a filter for the oscillations impressed upon the input circuit of the amplifier, thereby suppressing the harmonically related wave components produced by the distorting action of the device 1. It will also be appreciated that, due to the unidirectional properties of the device 2, variations in the impedance of the load circuit are prevented from reacting upon the frequency determining circuit of the oscillator.

lVhile in the preceding description'reference has been made to a particular circuit arrangement and specific details have been given. for the purpose of completely and clearly disclosing the nature of the invention, it is to be understood that the principles of this invention, as defined in the attached claims may be embodied in other arrangements.

What is claimed is:

1. A method of generating oscillations, by means of a three-electrode space discharge device having associated input and out ut circuits coupled in feed back relation, whlch comprises transmitting the entire oscillating output energy of the device through a -path adapted to limit to a predetermined value the amplitude of the oscillatory curfor coupling said oscillating current branch rent flowing through it, producing oscillations of selected frequency by the current travers ng said path, impressing the potential of selected frequency upon the control element of said device, and using said potential to control the operation of the amplifier.

3. An oscillation generator comprising an electric discharge device having an input circuit and an output circuit coupled in feed back relation, said output circuit embodying a feed back path, conveying only the oscillating current generated, which includesa high impedence device and a tuned circuit.

4. An oscillation generator comprising an electric discharge device having an input circuit and an output circuit coupled in feed back relation, said output circuit embodying a feed back path, conveying only the oscillating current generated, which includes a high resistance and a tuned circuit.

5. An oscillation generator comprising an electric discharge device, input and output circuits therefor, the output circuit having a direct current branch and an oscillating current branch, a high impedence device and a tuned circuit included in said oscillating current branch, and means for coupling said input circuit and said oscillating branch in feed back relation.

6. An oscillation generator comprising an electric discharge device, input and output circuits therefor, said output circuit having a direct current branch and an oscillating current branch, a high resistance and a tuned circuit included in said oscillating current branch, and means for coupling said input circuit and oscillating current branch in feed back relation.

v circuit in feed back relation.

8. An oscillation generator comprisi g a space discharge device and a unidirec ionally conductive amplifier each having input and output circuits, an oscillating current path for said device coupled in feed back relation to the input circuitsof said device and said amplifier, and a high resistance and a tuned circuit included in said oscillating current path.

9. An oscillation generator comprising a space discharge device and a unidirectionally conductive amplifier each having input and output circuits, the output circuit of said device having a direct current branch and an oscillating current branch, at high resistance and a tuned circuit included in said oscillating current branch and means to the input circuit of said device and to the input circuit of said amplifier.

10. An oscillation generator comprising a space discharge device and a unidirectionally conductive amplifier each having input and output circuits, the output circuit of said device having a direct current branch and an oscillating current branch, a high resistance and a tuned circuit included in. said oscillating current branch, and means for coupling said tuned circuit with the input circuits of said device and said amplifier.

11. An oscillation generator comprising a space discharge device and a unidirectionally conductive amplifier having the same physical characteristics, each having input and output circuits, the output circuit of said device having a space current path and an oscillating current path which includes a high resistance and a tuned circuit, and means for coupling said oscillating current path and the input circuits of said device and amplifier.

12. An oscillation generator comprising a space discharge device, and means for feeding back the oscillating output energy of said device to its input circuit through a path, separate from the space current path of the device, which includes a high resistance and a tuned circuit.

13. An oscillation generator comprising a space discharge device and a space discharge amplifier, and means for feeding back the oscillating output energy of said device to the input circuits of said device and said amplifier through a path, separate from the space current path of the device, which includes a high resistance and a tuned circuit.

14. An oscillation generator comprising a space discharge device having input and output circuits, a space discharge amplifier having an input circuit, a conductive path ,for the oscillating output energy of said device, separate from the space current path of the device, which includes a high resistance and atuncgl circuit. means for coupling said output path to the input circuit of said device, and a connection for impressing the resultant oscillating potential directly upon the input circuit of said amplifier.

1.5. An oscillation generator comprising a space discharge device and a space discharge amplifier each having a cathode, an anode and a control element, an input circuit connectin; the cathode and control element of said device, an output circuitconnecting the cathode and anode of said device, said output circuit having an oscillating current path, separate from the space current path, said input circuit and oscillating current path being connected in feed back relation, a high resistance and a frequency determining circuit included in said oscillating curill) and capacity constituting a frequency-determining circuit, said inductance having a high time constant, and an input circuit including a coil inductively associated with said inductance.

17. An oscillation generator comprising an electric discharge device, input and out- I put circuits therefor, the output circuit having separate direct and oscillating current branches, a high resistance and a tuned circuit comprising an inductance and a capacity included in said oscillating current branch, the time constant of said inductance being high, and a coil included in the input circuit associated with said inductance for coupling said input and tuned circuits in feed back relation, the coefiicient of coupling between said inductance and said coil being high.

18. An oscillation generator comprising a space discharge device and a space discharge amplifier each having input and output circuits, the output circuit of said devi having separate direct and oscillating current branches, a high resistance and parallel connected inductance and capacity-constituting a tuned circuit included in said oscillating current branch, said inductance having a high time constant, a coil included in the input circuit of said device and said amplifier and inductively associated with said inductance.

19. An oscillation generator comprising a space discharge device and a space discharge amplifier each having input and output circuits, the output circuit of said device having a direct current branch and an oscillating current'branch including a'high resistance and parallel connected inductance and capacity constituting a tuned circuit, said inductance having a high time constant, a coil included in the input circuit of said device and said' amplifier and inductively associated with said inductance, the coefficient of coupling between said inductance and said-coil being high.

In witness whereof, I hereunto subscribe my name this 17th day of April A. D., 1922.

JOSEPH W. HORTON. 

